1. Field of the Invention
The invention relates especially to an integrated antenna system in space telecommunications for mobile terrestrial stations (Satcom).
It can also be used in related fields such as radars or RF beams whenever the antenna system is in motion relative to its carrier.
In space telecommunications using the C, X, Ku, Ka, Q and other bands, with existing geostationary satellites, the mobile terrestrial stations are supposed to be equipped with an agile antenna automatically aimed at the traffic satellite, whatever its position in the sky (all the elevation angles from 0 to 90°, all the relative bearing angles from 0 to 360°).
In the description, the vertical and horizontal directions are referenced in the figures. They relate for example to a ground assumed to be horizontal and plane, referenced S, or again a place in which the antenna is positioned.
2. Description of the Prior Art
FIG. 1 exemplifies a commonly used prior-art antenna system. The antenna is a motor-driven parabolic antenna 1, herein represented with its main reflector 2 and its source 3. The assembly is protected by a radome 4. FIG. 1 shows the antenna in three positions of elevation, respectively a horizontal position, a 45° position and a vertical position. The internal volume of the radome 4 is mostly occupied by the antenna 1 and its displacement. All things considered, there therefore remains little space to house the equipment associated with the antenna, such as the drive system, the power amplifier, the low-noise amplifier, the transpositions and all the equipment habitually associated with the working of an antenna. A part of these devices is sometimes transferred into other compartments of the station, often in an inconvenient way.
Another prior art solution consists of the use of an electronically scanned antenna 5, as shown in FIG. 2. This type of antenna especially has the properties of being plane and of being capable of electronically deflecting its beam along an axis “A”. FIG. 2 shows an antenna performing an electronic scan 6 in elevation and a mechanical deflection in relative bearing 7. Relative to the antenna of FIG. 1, there is no longer any antenna displacement. In comparing FIG. 1 and FIG. 2, it is noted that a major part of the volume initially occupied by the displacement of the antenna is freed and therefore made available (this is the volume referenced 8 in the figure).
This approach nevertheless comes up against difficulties relative to the electronically scanned antenna, namely cost, performance, etc.
The antenna system according to the invention relies on a novel approach which judiciously uses a flat antenna whose antenna beam is fixed but deflected from the mechanical axis of the antenna, this beam being also inclined relative to a main mechanical axis.